Clegg has killed the Tories' hopes of a majority

The loss of the boundary changes is disastrous for Cameron.

Nick Clegg said the Conservatives had broken the coalition agreement by refusing to support House of Lords reform. Photograph: Getty Images.

A mournful Nick Clegg has just confirmed that the coalition will not proceed with House of Lords reform after David Cameron failed to persuade enough Tory MPs to renege on their opposition to the bill. "Part of our contract has now been broken," he lamented. Clegg went on to announce that the Lib Dems would retaliate by voting against the boundary changes, which would gift the Tories an extra 20 seats, when they reach Parliament. Without the support of Clegg's MPs, who, after all, account for 100 per cent of the government's majority, the reforms are effectively dead.

The key political consequence of this is that it will now be even harder for the Conservatives to win a majority in 2015. As I've noted before, with the boundary changes, the Tories would have needed a lead of seven points (on a uniform swing) to win a majority. Without them, they need a lead of 11 points. Conversely, Labour, which would have required a lead of four points with the boundary changes, now needs a lead of just three.

The reason Labour retain their electoral advantage is that the electoral bias towards the party owes more to differential turnout (fewer people tend to vote in Labour constituencies) and regional factors (the Tory vote is poorly distributed) than it does to unequal constituencies (the coalition planned to fix constituency sizes at around 76,000 voters).

Even with the boundary changes, a Tory majority in 2015 was looking unlikely. No sitting prime minister has increased their party's share of the vote since 1974, and Cameron is failing to make progress among those groups that refused to support him last time round. Now, with the loss of the reforms, the challenge of building a Tory majority has moved from "difficult" to "impossible".

Ironically, after the opprobrium heaped on him by Labour, it is Clegg, in blocking the boundary changes, who has done Miliband's party the greatest possible service.